exhaust manifold casting numbers

Could some one please decode these casting numbers for me
Driver side 3751084-1 B 12-19-72

Passenger side 3830684 AG 12-16-74

Thanks in advance
Kevin

They are off a small block. I had them on my 74 Challenger with a factory 360. I know they are not from the challenger. When I bought the car in 97 the car had headers. I put the manifolds on when I pulled the headers off but can't remember what or where I got them from(getting old sucks). I have given the car to my son and we have since put headers back on and I had these lying around and thought I'd see I could find out what there from. I have googled them but come up with nothing.

the 3751084 number is 1973-1974 drivers side E, B body. the other number you have, I'm thinking by the date code, is a 1975. you can tell the 1975 and newer manifolds, as they have verticle reinforcement ribbing on them...like 5 or 6 ribs?? I would be interested in purchasing that 3751084 manifold from you; gregory_m56312@yahoo.com or I.M. me back